The present invention relates to a printer for printing an image on a sheet while conveying the sheet and more particularly to a method of correcting a sheet conveyance error and an apparatus therefor.
Printers extensively used today include a printer of the type using a continuous sheet made up of a train of segments. Each segment of this kind of sheet is provided with a respective segment mark beforehand. The problem with this type of printer is that by simply sensing the segment mark of the first segment to cause it to start at a preselected position, it is impossible to prevent an image from being shifted on the last segment. Because the shift of an image is ascribable even to the varying environment and the deterioration of a platen, it cannot be obviated by mechanical adjustment. Moreover, a conveyance error is apt to occur due to, e.g., an error in the diameter of the platen. Such errors would accumulate and also bring about the shift of an image.
In light of the above, it has been proposed to correct a conveyance error at the time of starting a new line. Japanese Patent Laid-Open Publication Nos. 63-1352277 and 63-137876, for example, each teach a system that provides a printing medium with marks and correct the positional error of a new line at the time of printing without regard to the kind of a new line pitch or the amount of a new line. However, the new line width corrected by the systems taught in the above documents is constant, so that an odd conveyance error of, e.g., xc2xd step and ⅓ step cannot be corrected. The systems therefore cannot obviate the shift of an image and make it difficult to print an image at the preselected position of a preselected format.
It is therefore an object of the present invention to provide a method capable of correcting the conveyance error of a sheet to thereby insure constant, accurate conveyance, and an apparatus therefor.
It is another object of the present invention to provide a printer capable of conveying a sheet constantly and accurately and easily printing an image at the preselected position of a preselected format.
In accordance with the present invention, a method of correcting the conveyance error of a continuous sheet having a train of segments each including the respective segment mark and being conveyed for printing in accordance with the number of steps begins with a step of counting the steps between consecutive segment marks during conveyance of the sheet to thereby output an actual number of steps. The actual number of steps is compared with a preselected number of steps determined by a distance between the consecutive segment marks to thereby output a result of comparison. The start of a new line is corrected on the basis of the result of comparison at even positions of a single segment during subsequent conveyance.
Also, in accordance with the present invention, an apparatus for correcting the conveyance error of a continuous sheet having a train of segments each including the respective segment mark and being conveyed for printing in accordance with a number of steps includes a counting section for counting the steps between consecutive segment marks during conveyance of the sheet to thereby output an actual number of steps. A comparing section compares the actual number of steps with a preselected number of steps determined by a distance between the consecutive segment marks to thereby output a result of comparison. A correcting section corrects, based on the result of comparison, the start of a new line at even positions of a single segment during subsequent conveyance.